1. Field of the Invention
The present invention relates to a lens barrel. More particularly, this invention is concerned with a lens barrel adaptable to a camera of a collapsible type photographic lens or a two-focus type, and a camera with a macro zoom function. The camera of a collapsible type photographic lens or a two-focus type has a plurality of moving frames, which hold groups of photographic lenses, moved independently along the optical axis of the lenses, and thus assumes two different states.
2. Description of the Related Art
Photography apparatuses include a typical compact camera for performing photography using, for example, a silver film, and an electronic still camera (hereinafter an electronic camera) for recording an image signal, image information, or the like output from an imaging means such as a CCD. The photography apparatuses (hereinafter these types of cameras are generically called cameras) are normally carried in one's bag or the like for use. What counts for much in designing the cameras is therefore how to improve portability.
Among members constituting such a camera, a lens barrel occupies a large portion of the camera in terms of volume and weight. The lens barrel is composed of a plurality of lens frames for holding a photographic optical system so that the photographic optical system can move along the optical axis thereof. When the lens barrel itself is designed compactly, it will contribute greatly to realization of a compact camera and improvement of portability.
In recent years, a so-called variable-power photographic optical system (hereinafter a zoom lens) capable of continuously varying its focal length has been widely adopted as a photographic optical system employed in cameras. Moreover, there is an increasing demand for higher powers or higher zooming ratios.
However, numerous photographic lenses and numerous lens frames for holding the photographic lenses are needed to construct a zoom lens barrel. The number of members constituting the zoom lens barrel increases, contrary to the trend towards a compact zoom lens barrel. Furthermore, when an attempt is made to realize a zoom lens offering a high power, the lens barrel tends to get large.
For improving the portability of cameras while adopting a zoom lens, various means including a photographic lens-collapsible lens barrel have been proposed and put to practical use. The photographic lens-collapsible lens barrel can be set to two states by moving a plurality of lens frames. The two states are a photographic state in which photography can be performed and a non-photographic state (collapsed state) in which a camera is being carried.
In the cameras, when photography is carried out, part of the lens barrel is thrust out from the face of a camera body (photographic state). When the camera is being carried or photography is not carried out, the plurality of lens frames constituting the lens barrel is moved independently in order to narrow the spacing between adjoining ones of the lens frames. Moreover, the lens barrel itself is stowed in the camera body (collapsed).
In the photographic lens-collapsible cameras, when photography is not carried out, the spacing between adjoining ones of the plurality of lens frames to be stowed in the lens barrel must be narrowed as much as possible. It is therefore necessary to make the overall length of the photographic optical system as short as possible.
However, when the overall length of the photographic optical system in the lens barrel employed in the conventional collapsible cameras is made as short as possible, a moving mechanism and a restricting member are required. The moving mechanism helps move all the moving frames out of the plurality of lens frames, which can move along the optical axis thereof, from positions predetermined for photography to positions predetermined for non-photography. The restricting member restricts turning of the moving mechanism.
In this case, the magnitudes of movements made by the moving frames and the movements of the moving frames are different mutually. Each moving frame must therefore be provided with an independent moving mechanism and restricting member. This poses problems. Specifically, since the moving mechanisms realized with cam mechanisms or the like must be arranged in the lens barrel, the lens barrel must be made large. Moreover, the lens barrel must be large enough to accommodate the complex mechanisms and the camera using the lens barrel must also be designed large. Besides, the cost of manufacturing increases.
For avoiding the problems, moving frames that contribute little to shortening of the overall length of the photographic optical system are not provided with a dedicated moving mechanism. The moving frames are designed not to be able to move (fixed). This is a conventionally adopted means. Thus, efforts have been made to eliminate factors making the lens barrel larger. However, the effect of the means is limited.
Moreover, in the conventional lens barrel for the photographic lens-collapsible cameras, a guide shaft composed of a plurality of elongated axes is usually used as a movement restricting member. The movement restricting member supports the moving frames including the lens frames that move in the lens barrel, guides the movements along the optical axis of the moving frames, and restricts the turnings of the moving frames.
However, when the guide shaft is used as the movement restricting member for restricting the movements of the moving frames, the guide shaft itself and a bearing member for bearing the guide shaft must be arranged along the optical axis. This becomes a factor of obstructing realization of a compact and short lens barrel.
Moreover, the guide shaft composed of elongated axes is placed in a locking frame for supporting the moving frames arranged in the lens barrel. This poses a problem in that the layout of the moving frames and the movable range thereof are limited.
In an effort to shorten the lens barrel, a means for shortening the guide shaft has been proposed in, for example, Japanese Patent Application No. 7-174956. Specifically, a lens frame interposed between two lens frames holding two groups of photographic lenses is provided with a bearing for bearing the guide shaft.
On the other hand, an effort has been made to independently move the moving frames including a plurality of lens frames along the optical axis. Specifically, a cam frame serving as a substantially cylindrical moving mechanism has generally been employed in conventional lens barrels. The cam frame used in practice has a plurality of cam grooves formed on the outer circumference thereof so that it can drive three or more moving frames including lens frames. The cam grooves are shaped to match the moving frames. Cam pins or the like formed on the plurality of moving frames are engaged with the plurality of cam grooves.
In this case, the plurality of cam grooves is formed on the outer circumference of the cam frame. This poses a problem in that the rigidity of the cam frame itself deteriorates. For ensuring the required rigidity for the cam frame itself, it is necessary to increase the thickness of a cylindrical member used to form the cam frame.
On the other hand, as for conventional lens barrels, a proposal has been made to decrease the diameter of a lens barrel for realizing a compact lens barrel.
For example, a lens barrel proposed by the present applicant is described in Japanese Patent Application No. 9-244371. In this case, a driving means such as a motor or a driving force conveying mechanism, which drives a cam frame, is stowed in a locking frame for supporting the cam frame. A gear portion for driving the cam frame is formed on the inner circumference of the cam frame. A driving output of the driving means is conveyed to the gear portion on the cam frame by way of the driving force conveying mechanism. The cam frame is thus turned.
Furthermore, according to the Japanese Patent Application No. 9-244371, a moving frame for holding any member other than groups of photographic lenses, for example, a motor holding frame for holding an AF motor is arranged along the optical axis together with other lens frames. A guide shaft serving as a direction-of-movement restricting member is attached to a moving frame such as the motor holding frame. The guide shaft is utilized in order to restrict the movements of moving frames such as lens frames located before and after the moving frame such as the motor holding frame.
In the conventional lens barrels, a cylindrical member used to form a cam frame may be made thicker so that the cam frame itself can maintain required rigidity. In this case, the dimension in a radial direction of the lens barrel gets larger. Consequently, the lens barrel gets larger.
Moreover, when the gear portion is, like that in the means proposed in the Japanese Patent Application No. 9-244371, formed on the inner circumference of the cam frame, it will contribute to a decrease in diameter of a lens barrel. However, the layout of cam grooves to be cut in the inner circumference of the cam frame may be limited. Since the cam grooves and gear portion are formed in and on the inner circumference of the cam frame, the structure of dies used to manufacture the cam frame gets complex. This leads to an increase in cost of manufacturing.
Furthermore, the moving frame for holding an AF motor may be arranged on the optical axis together with other moving frames including a plurality of lens frames. This poses a problem in that the overall length of the lens barrel increases.
On the other hand, aside from the conventional photographic lens-collapsible cameras, there are a so-called two-focus camera and a so-called macro zoom selectable camera. In the two-focus camera, a lens barrel to be set to two states by moving the moving frames including a plurality of lens frames can selectively offer two focal lengths. The macro zoom selectable camera selectively enables normal photography and macro zoom photography. Normal photography is carried out with a lens barrel located in a normal photography zone. Macro zoom photography is carried out with the lens barrel located in a photography zone located closer to an object, that is, in a macro zoom zone. These lens barrels have an independent moving mechanism provided for every plurality of moving frames that move along the optical axis. Various kinds of such lens barrels have been put to practical use in the past.
However, members other than a photographic optical system, for example, component members of a shutter mechanism and diaphragm mechanism are incorporated in a lens barrel in any conventional camera. In this case, these component members may be united with a lens frame or locked at predetermined positions in the lens barrel.
In the lens barrels employed in the cameras having the collapsing mechanism, two-focus mechanism, and macro zoom mechanism, a moving mechanism for moving the moving frames to be arranged in a lens barrel may be simplified in order to design the lens barrel compactly. However, this poses a problem in that such component members as the shutter mechanism and diaphragm mechanism cannot help being placed at positions in a lens barrel that are not always optimal in terms of optical designing.